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Family Rissoellidae Rissoellids
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The Rissoellidae is a family of minute molluscs with simple, unadorned shells found living mainly on algae in the lower littoral and shallow sublittoral zones. The family occurs world-wide; it occurs in the Indo-West Pacific, including tropical and temperate Australia, and extends southwards to the Antarctic. Rissoellids feed on diatoms, algal filaments and some detritus. Some species are common in NSW, and are easily obtained by washing intertidal algae. Members of the Rissoellidae are hermaphrodites, producing hemispherical egg capsules from which crawling young emerge. The protoconch is homeostrophic i.e, it is coiled about the same axis as the teleoconch. The family in Australia was poorly know until Ponder & Yoo (1977) reported on the animal and shell morphology, animal anatomy and radular characters. They considered the family to have only one genus Rissoella which they divided into four subgenera based mainly on radular characters. (In this treatment the subgenera are not used). There are 14 species known from Australia, four of which are from NSW. One of these was named by Iredale in 1912, another by Finlay in 1924, and the other two species by Ponder & Yoo in 1977. Family Reference Ponder, W.F. & Yoo, E.K. 1977. A revision o0f the Australian species of the Rissoellidae. (Mollusca: Gastropoda). Records of the Australian Museum 31 (4): 133–185. Coverage Al the named species of the family from NSW are detailed here. Identification Notes Shells can be placed in this family by their small size - up to 3 mm in height - globose form with umbilicus closed or only narrowly open, and smooth surface. Shells of approximately similar form occur in the Skeneidae, (but these are usually not smooth), Cingulopsidae, Eatonillidae, Rissoidae and Tornidae.
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